Page 306 - Atlas of Small Animal CT and MRI

296 Atlas of Small Animal CT and MRI

because of the peripheral displacement of fracture frag­ Sacral trauma
ments (Figure 3.2.3). Atlantal wing fractures are often A sacral fracture classification system has been proposed,
mildly displaced as the result of traction forces from which classifies fractures as alar, foraminal, transverse,
muscle attachments (Figure 3.2.4). avulsion, and comminuted, with transverse fractures
making up about half of all sacral fractures in both dogs
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Axial (C2) fractures and cats. A simpler scheme distinguishes abaxial
Odontoid process (dens) fractures are usually caused by fractures, those that occur lateral to the sacral foramina,
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cervical hyperflexion/hyperextension and atlantoaxial mal­ from axial fractures. Fractures that involve the sacral
formations with pre‐existing instability predisposed to the foramina and canal are more likely to result in clinically
injury. Fractures of the odontoid process are easily detected significant neurologic deficits. A majority of patients
on both CT and MR images because the cranial fracture with sacral fractures also have complex orthopedic
fragment is often displaced (Figures 3.2.5, 3.2.6). The MR injuries, including sacroiliac luxation and other pelvic
appearance of the ligaments of the normal canine occip­ fractures (Figures 3.2.15, 3.2.16). 15,16
itoatlantoaxial region has been described, and ligaments
were hypointense on all sequences. Close inspection of Traumatic intervertebral disk extrusion
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the integrity of the ligaments may be useful in determining Intervertebral disk extrusion can occur as the direct
the stability of traumatic lesions in this region. result of trauma and can be either compressive or non­
Fractures of the axial body, arch, and spinous process compressive. Both normal disks and those with nuclear
also occur, with the integrity of atlantoaxial stability degeneration are at risk, but degenerate disks more often
dependent on the specific nature of the fracture lead to spinal cord compression. Normal nucleus pulpo­
(Figure 3.2.7). C2 fractures are referred to as burst fractures sis is composed predominantly of water, and when herni­
when comminuted and the result of compressive forces. ated through the annulus, fibrosis can dissipate into the
epidural fat or through the dura mater and into the spinal
Caudal cervical (C3–C7) vertebral fractures cord. This can result in an intrinsic spinal cord lesion
and luxations with no overt evidence of compression. Because degener­
Fractures and luxations of the third through seventh ate nucleus pulposis contains more solid mass, traumatic
cervical vertebrae are less common than C1 and C2 extrusion is more likely to result in spinal cord compres­
injuries and are caused more often by bite injury than sion. 17–19 CT features of traumatic intervertebral disk
motor vehicle trauma (Figures 3.2.8). 9 extrusion include disk space narrowing with or without
extradural spinal cord compression. The latter feature is
best seen using CT myelography. The MR features of
Thoracolumbar fracture/luxation traumatic intervertebral disk extrusion in dogs include
Between 49% and 58% of vertebral fracture/luxations
involve the T3–L3 region in dogs and cats, and reduced volume and T2 signal intensity of the affected
disk and increased spinal cord T2 intensity at the level of
24–38% involve the L4–L7 region. Most fractures in
this region are associated with clinically significant disk extrusion. Extrusion of degenerate disk material is
more likely to result in an extradural compressive mass
neurologic deficits. 8,13 Motor vehicle trauma has been 17–19
reported as the most common cause for thoracolum­ (Figure 3.2.17).
bar fracture/luxation in dogs, whereas cats are just as
likely to sustain injuries from a fall. Although there Spinal cord trauma
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are some differences between cats and dogs, vertebral
luxation or fracture/luxation has been reported to be Contusion/hemorrhage
the most common injury for both, followed by wedge Spinal cord trauma is usually but not always accompanied
compression fractures, transverse fractures, and sub­ by overt vertebral column trauma. Neurologic deficits
luxation and hyperextension injuries. Multiple com­ range from clinically silent to complete spinal cord
partments are involved in the majority of injuries; transection. In addition to the primary spinal cord
endplate involvement is seen in approximately a third, injury that results directly from trauma, secondary
and rotational displacement and intervertebral space injury occurs from vascular damage, local cytotoxic
involvement is present in more than half. Fracture/ biochemical responses to injury, and inflammatory
13
luxation also occurs with greater frequency at junc­ response, the combination of which can lead to progres­
tions between mobile and less mobile regions of the sive disease. Postmortem examination of spinal cords
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vertebral column (Figures 3.2.9, 3.2.10, 3.2.11, 3.2.12, of dogs and cats that sustained traumatic injury revealed
3.2.13, 3.2.14). 14 thoracolumbar necrosis that correlated with the degree

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